Vapor phase catalytic process for simultaneous furfural hydrogenation and cyclohexanol dehydrogenation

ABSTRACT

The present invention provides a catalytic process for the synthesis of furfuryl alcohol and cyclohexanone simultaneously over a copper based catalyst in vapour phase conditions by hydrogenation of furfural and dehydrogenation of cyclohexanol respectively.

FIELD OF THE INVENTION

The present invention relates to a catalytic process for simultaneousfurfural hydrogenation and cyclohexanol dehydrogenation in vapor phase.

BACKGROUND OF THE INVENTION

Furfuryl alcohol is an important chemical, mainly used for theproduction of resins for bonding foundry sand to produce cores and moldsfor metal casting, corrosion-resistant mortar for installing acid proofbrick, laminating resins for corrosion resistant fiberglass-reinforcedequipment, resins for corrosion resistant furan polymer concrete,impregnating solutions and carbon binders. It is also used asnonreactive diluent for epoxy resins, modifier for phenolic and urearesins, oil-well sand consolidation, solvent, production of tetrahydrofurfuryl alcohol and other chemical synthesis. It is also an importantchemical intermediate for the manufacture of lysine, vitamin C,lubricant, dispersing agent and plastisizer.

Cyclohexanone is an industrially important chemical for the manufactureof caprolactum and adipic acid which are used in producing polyamidefiber in nylon-textiles.

Industrially, furfuryl alcohol is produced by hydrogenation of furfuraleither in liquid phase or in vapor phase. On the other hand,cyclohexanone is produced majorily in vapor phase by dehydrogenation ofcyclohexanol. Both the processes employ copper based catalysts.

A number of methods are reported in patent literature on the preparationof catalysts useful for the separate hydrogenation of furfural anddehydrogenation of cyclohexanol.

Liquid phase hydrogenation of furfural under a pressure of 30 atm. overcopper chromite catalysts were disclosed in U.S. Pat. Nos. 4,251,396,4,302,397. Chinese patent CN1404922 discloses a catalyst comprising ofCuO—Cr₂O₃—NiO for the liquid phase hydrogenation of furfural at 35 to 50atm. and in the temperature range of 453–473 K. The vapor phasehydrogenation of furfural was disclosed in U.S. Pat. Nos. 4,261,905 and5,591,873 wherein copper chromite promoted with alkali earth metals andcopper deposited on pyrogenic SiO₂ respectively were employed ascatalysts. In both the cases the reaction was carried out underpressure.

Vapour phase dehydrogenation of cyclohexanol to produce cyclohexanoneover Cu—Cr based catalysts are disclosed in KR8300880 and U.S. Pat. No.4,310,703. Processes for making Cu/ZnO or Cu/SiO₂ with promoters,suitable for dehydrogenation of cyclohexanol were disclosed inJP2000288395, RU210183, U.S. 2004087815, WO09810864. Process for makinga multicomponent Cu based cyclohexanol dehydrogenation catalyst wasdisclosed in CN1056067. A process for making Cu on MgO with promotersfor dehydrogenation reaction was disclosed in CN1235870. Liquid phasedehydrogenation of cycloheaxanol under pressure was disclosed in Chinesepatent CN1381434 and the corresponding method for catalyst making wasdisclosed in another Chinese patent CN1381435. A process for making anon Cu based catalyst comprising of ZnO—CaO or CaCO₃—Cr₂O₃ is disclosedin U.S. Pat. No. 6,376,422.

A process for making Cu based catalyst suitable for both hydrogenationand a dehydrogenation process separately was disclosed in GB patent1097819.

The main drawbacks of the furfural hydrogenation processes mentionedabove are that they require either to be operated under pressure or touse large amount of hydrogen along with furfural. Even though bothfurfural hydrogenation and cyclohexanol dehydrogenation processes employmostly Cu based catalysts, there are no reports on the combined orsimultaneous study of these two processes over a single catalyst system.

OBJECTS OF THE INVENTION

The main object of the invention is to provide a catalytic process forsimultaneous furfural hydrogenation and cyclohexanol dehydrogenation invapor phase conditions.

Another object of the invention is to provide a process wherein the useof external source of hydrogen is avoided for furfural hydrogenation dueto self-generation of hydrogen, thereby saving on costs.

Another object of the invention is to provide a process whereinsimultaneous furfural hydrogenation and cyclohexanol dehydrogenationtakes place at atmospheric pressure.

Still another object of the invention is to provide a process whereinthe equilibrium barrier for the dehydrogenation of cyclohexanol can beovercome.

Yet another object of the invention is to provide a process wherein thevapor phase hydrogenation of furfural and dehydrogenation ofcyclohexanol are conducted on a copper-magnesia promoted by chromiacatalyst prepared by simple techniques like coprecipitation and/orimpregnation.

Another object of the invention is to provide a process with stablecatalytic activity in simultaneous furfural hydrogenation andcyclohexanol dehydrogenation.

SUMMARY OF THE INVENTION

The present invention provides a catalytic process for the synthesis offurfuryl alcohol and cyclohexanone simultaneously over a copper basedcatalyst in vapour phase conditions by hydrogenation of furfural anddehydrogenation of cyclohexanol respectively.

Accordingly the present invention provides a catalytic process for thesimultaneous synthesis of furfuryl alcohol and cyclohexanone by thehydrogenation of furfural and dehydrogenation of cyclohexanolrespectively, the process comprising contacting a mixture of furfuraland cyclohexanol with a copper based catalyst of the formulaxCu—yMgO—zCr₂O₃, wherein x, y and z are the amounts in terms of weightpercent of Cu, MgO and Cr₂O₃ respectively, under reaction conditions,collecting product streams obtained and separating furfuryl alcohol andcyclohexanone.

In one embodiment of the invention, the copper based catalyst has a Cucontent in the range of 5 to 50 wt % preferably in the range of 10 to 25wt %. Cr₂O₃ content in the range of 0 to 15 wt %, preferably in therange of 1 to 10 wt %, the balance being MgO.

In another embodiment of the invention, co-precipitation method isemployed for preparing Cu—MgO and/or Cu—MgO—Cr₂O₃.

In another embodiment of the invention, the Cr₂O₃ is deposited onCuO—MgO by impregnation.

In yet another embodiment of the invention, the mixture of furfural andcyclohexanol is contacted with the copper based catalyst in vapor phaseresulting in the hydrogenation of furfural by hydrogen released due tothe dehydrogenation of cyclohexanol.

In another embodiment of the invention, the contacting is carried out ina quartz fixed bed vertical reactor (200 mm long and 8 mm i.d) placed inan electrically heatable cylindrical furnace, with about 1 g of thecatalyst packed at the center of the reactor between two plugs of quartzwool being reduced in 6% H₂ and balance He flow at 523 K for 4 hfollowed by lowering the temperature of the reactor to 473 K andreplacing the H₂/He by pure N₂ gas, the mixture of furfural andcyclohexanol being continuously pumped at a total liquid flow of 1 ml/hinto the reactor, the resulting product stream being separated intocyclohexanone and furfuryl alcohol.

In another embodiment of the invention, the contacting is carried out inthe absence of external hydrogen.

In yet another embodiment of the invention, the contacting is carriedout at a temperature of about 473 K and at atmospheric pressure.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the present invention involving hydrogenation offurfural and dehydrogenation of cyclohexanol processes over copper basedcatalysts, it is possible to conduct the two processes simultaneously.

The present invention resides in that no external source of hydrogen isrequired for the furfural hydrogenation, equilibrium barrier for thedehydrogenation of cyclohexanol can be overcome and since both thereactions are conducted in vapor phase, separation of catalyst fromproduct mixture is easy and the method of making the catalyst employssimple techniques like co-precipitation and impregnation.

In the process of the present invention the operation of both furfuralhydrogenation and cyclohexanol dehydrogenation at atmospheric pressureis disclosed. The equilibrium barrier for the dehydrogenation ofcyclohexanol is overcome. The copper based catalyst is prepared byrelatively simple techniques of co-precipitation and/or impregnation formaking of copper based catalyst. The catalytic activity is stable.

Scientific Explanation

Even though hydrogenation of furfural to yield furfuryl alcohol appearsto be simple, the nature of catalyst and the reaction conditions play animportant role particularly in getting furfuryl alcohol selectively.Copper based catalysts are suitable for this reaction. The reactiontemperature is critical and if it crosses a particular temperature (˜473K), ring hydrogenation may also lead to by-products.C₄H₄OCHO+H₂→C₄H₄OCH₂OH  (1)

Thus for getting one mole of furfuryl alcohol, one mole of furfural andone mole of hydrogen molecule are required. Also two moles of reactantsyield one mole of product and therefore this reaction is favorable underpressure.

On the other hand, dehydrogenation of cyclohexanol to cyclohexanone islimited by equilibrium constraints.C₆H₁₁OH⇄C₆H₁₀O+H₂  (2)

It was reported that the equilibrium conversion of directdehydrogenation of cyclohexanol (Ref: H. A. Cubberley and M. B. Muller,J. Am. Chem. Soc., 63 (1947) 1535) at 473 K was 45.22%.

The advantage of combining these two reactions are, that there is everypossibility to overcome the equilibrium limitations in the secondreaction and the hydrogen produced in the second reaction is sufficientto carryout the first reaction thereby there is no necessity to pumpextra hydrogen externally for the first reaction.

The catalyst employed in this investigation is Cu—MgO—Cr₂O₃ wherein theCu content is in the range of 5 to 50 wt. % preferably in the range of10 to 25 weight percent. Cr₂O₃ content is 0 to 15 weight percentpreferably in the range of 1 to 10 weight percent and the remaining isMgO. Coprecipitation method is employed for preparing Cu—MgO and/orCu—MgO—Cr₂O₃ because by this method it is possible to get moreCuO—MgO—Cr₂O₃ interacted species. Cr₂O₃ can also be deposited on CuO—MgOby impregnation technique.

Vapor phase hydrogenation of furfural was carried out in a quartz fixedbed vertical reactor (200 mm long and 8 mm i.d) placed in anelectrically heatable cylindrical furnace. About 1 g of the catalystpacked at the center of the reactor between two plugs of quartz wool hasbeen reduced in 6% H₂ (and balance He) flow at 523 K for 4 h followed bylowering the temperature of the reactor to 473 K and replacing the H₂/Heby pure N₂ gas. Mixture of furfural and cyclohexanol (total liquid flowof 1 ml/h) with the help of a syringe pump is continuously pumped. Theproduct mixture is collected in a receiver kept in an ice bath and it isanalyzed at regular intervals by gas chromatograph with flame ionizationdetector.

The present invention is described with reference to the followingexamples that are explained by way of illustrations only and should nottherefore be construed to limit the scope of the present work.

EXAMPLE—1

Approximately 230 ml of aqueous solution containing 8.36 g and 49.358 gof Cu(NO₃)₂.3H₂O and Mg(NO₃)₂.6H₂O respectively have been simultaneouslyprecipitated using an aqueous solution containing 1M K₂CO₃ at a pH of 9.The coprecipitated mass was thoroughly washed with distilled water forthree times and filtered. The resultant mass was impregnated with 2 mlof aqueous solution containing 0.53 g of Cr(NO₃)₃.9H₂O. The excess waterwas evaporated over a hot water bath and the sample was then driedovernight in an oven at 383 K followed by calcination in air at 723 Kfor 4 h.

This catalyst has been tested for furfural hydrogenation andcyclohexanol dehydrogenation simultaneously. In the activity experiment,the molar ratio of furfural and cyclohexanol is maintained at 1:5.Following are the results obtained.

Selectivity Selectivity of of furfuryl cyclo- alcohol, % Cyclo-hexanone, % Furfural (w.r.t. hexanol (w.r.t. S. Reaction conversion,furfural con- cyclohexanol No. Time, h % conversion) version, %conversion) 1 1 100 100 58.2 100 2 2 89.5 100 49.0 100 3 3 83.4 100 42.6100

EXAMPLE—2

The catalyst mentioned in example—1 has been tested for the furfuralhydrogenation and cyclohexanol dehydrogenation simultaneously. In theactivity experiment, the molar ratio of furfural and cyclohexanol ismaintained at 1:3.5. Following are the results obtained.

Selectivity Selectivity of of furfuryl cyclo- alcohol, % Cyclo-hexanone, % Furfural (w.r.t. hexanol (w.r.t. S. Reaction conversion,furfural con- cyclohexanol No. Time, h % conversion) version, %conversion) 1 1 70.8 100 58.4 100 2 2 76.3 100 49.2 100 3 3 78.3 10049.1 100

EXAMPLE—3

The catalyst mentioned in example—1 has been tested for the furfuralhydrogenation and cyclohexanol dehydrogenation simultaneously.

In the activity experiment, the molar ratio of furfural and cyclohexanolis maintained at 1:1.7. Following are the results obtained.

Selectivity Selectivity of of furfuryl cyclo- alcohol, % Cyclo-hexanone, % Furfural (w.r.t. hexanol (w.r.t. S. Reaction conversion,furfural con- cyclohexanol No. Time, h % conversion) version, %conversion) 1 1 76.8 100 50.6 100 2 2 63.8 100 37.7 100 3 3 57.8 10025.6 100

EXAMPLE—4

Approximately 222 ml of ethanol solution containing 8.36 g, 47.45 g and2.11 g of Cu (NO₃)₂. 3H₂O, Mg (NO₃)₂. 6H₂O and Cr(NO₃)₃. 9H₂Orespectively have been simultaneously precipitated using 20 weight %tetraethylammonium hydroxide solution at a pH of 9. The coprecipitatedmass has been thoroughly washed with ethanol for three times andfiltered. The sample was then dried in an oven at 383 K for overnightfollowed by calcination in air at 723 K for 4 h.

This catalyst has been tested for the furfural hydrogenation andcyclohexanol dehydrogenation simultaneously. In the activity experiment,the molar ratio of furfural and cyclohexanol is maintained at 1:5.Following are the results obtained.

Selectivity Selectivity of of furfuryl cyclo- alcohol, % Cyclo-hexanone, % Furfural (w.r.t. hexanol (w.r.t. S. Reaction conversion,furfural con- cyclohexanol No. Time, h % conversion) version, %conversion) 1 1 60.1 100 36.5 100 2 2 80.4 100 40.5 100 3 3 83.3 10041.0 100 4 4 88.4 100 39.5 100 5 5 87.7 100 37.1 100 6 6 88.8 100 34.7100 7 7 88.2 100 36.5 100

EXAMPLE—5

The catalyst mentioned in example—1 has been tested for the furfuralhydrogenation. In the activity experiment, furfural (liquid) and H₂(gas) feed rates are maintained at 1.2 ml/h and 11/h respectively andthe reaction temperature is maintained at 453 K. Following are theresults obtained.

Furfural Selectivity of S. Reaction conversion, furfuryl alcohol, % No.Time, h % (w.r.t. furfural conversion) 1 1 82.0 100 2 2 80.9 100 3 378.4 100 4 4 77.4 100 5 5 77.1 100 6 6 77.0 100

EXAMPLE—6

The catalyst mentioned in example—1 has been tested for the furfuralhydrogenation. In the activity experiment, furfural (liquid) and H₂(gas) feed rates are maintained at 2 ml/h and 11/h respectively and thereaction temperature is maintained at 473 K. Following are the resultsobtained.

Furfural Selectivity of S. Reaction conversion, furfuryl alcohol, % No.Time, h % (w.r.t. furfural conversion) 1 1 60.2 100 2 2 61.0 100 3 357.9 100 4 4 63.5 100 5 5 58.3 100 6 6 59.6 100

EXAMPLE—7

The catalyst mentioned in example—1 has been tested for the cyclohexanoldehydrogenation.

In the activity experiment, cyclohexanol (liquid) and N₂ (gas) feedrates are maintained at 1 ml/h and 0.521/h respectively and the reactiontemperature is maintained at 453 K. Following are the results obtained.

Cyclohexanol Selectivity of S. Reaction conversion, cyclohexanone, % No.Time, h % (w.r.t. cyclohexanol conversion) 1 1 34.2 100 2 2 31.8 100 3 330.8 100 4 4 30.4 100 5 5 30.9 100 6 6 31.7 100

EXAMPLE—8

The catalyst mentioned in example—1 has been tested for the cyclohexanoldehydrogenation.

In the activity experiment, cyclohexanol (liquid) and N₂ (gas) feedrates are maintained at 1 ml/h and 0.521/h respectively and the reactiontemperature is maintained at 473 K. Following are the results obtained.

Cyclohexanol Selectivity of S. Reaction conversion, cyclohexanone, % No.Time, h % (w.r.t. cyclohexanol conversion) 1 1 44.2 100 2 2 37.9 100 3 340.9 100 4 4 40.9 100 5 5 41.2 100 6 6 38.7 100

EXAMPLE—9

The catalyst mentioned in example—1 has been tested for the cyclohexanoldehydrogenation.

In the activity experiment, cyclohexanol (liquid) and N₂ (gas) feedrates are maintained at 1 ml/h and 0.521/h respectively and the reactiontemperature is maintained at 498 K. Following are the results obtained.

Cyclohexanol Selectivity of S. Reaction conversion, cyclohexanone, % No.Time, h % (w.r.t. cyclohexanol conversion) 1 1 52.2 100 2 2 53.8 100 3 356.8 100 4 4 55.8 100 5 5 53.2 100 6 6 54.9 100

EXAMPLE—10

The catalyst mentioned in example—1 has been tested for the cyclohexanoldehydrogenation.

In the activity experiment, cyclohexanol (liquid) and N₂ (gas) feedrates are maintained at 1 ml/h and 0.521/h respectively and the reactiontemperature is maintained at 523 K. Following are the results obtained.

Cyclohexanol Selectivity of S. Reaction conversion, cyclohexanone, % No.Time, h % (w.r.t. cyclohexanol conversion) 1 1 61.1 100 2 2 67.0 100 3 364.2 100 4 4 67.7 100 5 5 66.9 100 6 6 66.0 100

ADVANTAGES OF THE INVENTION

-   1. The process of the reaction comprises simultaneous hydrogenation    of furfural and dehydrogenation of cyclohexanol over a single    catalyst system.-   2. The contacting is carried out under atmospheric pressure and    under vapour phase conditions.-   3. External source of hydrogen for hydrogenation is not required    since hydrogen is generated during the contacting due to    dehydrogenation of cyclohexanol leading to saving in costs.

1. A catalytic process for the simultaneous synthesis of furfurylalcohol and cyclohexanone by the hydrogenation of furfural anddehydrogenation of cyclohexanol respectively, the process comprisingcontacting a mixture of furfural and cyclohexanol with a Cu basedcatalyst of the formula xCu—yMgO—zCr₂O₃, wherein x, y and z are theamounts in terms of weight percent of Cu, MgO and Cr₂O₃ respectively,under reaction conditions, collecting product streams obtained andseparating furfuryl alcohol and cyclohexanone.
 2. A process as claimedin claim 1 wherein the Cu based catalyst has a Cu content in the rangeof 5 to 50 wt %, Cr₂O₃ content in the range of 0 to 15 wt %, balancebeing MgO.
 3. A process as claimed in claim 2 wherein the copper basedcatalyst has a Cu content in the range of 10 to 25 wt %, Cr₂O₃ contentin the range of 1 to 10 wt %, the balance being MgO.
 4. A process asclaimed in claim 1 wherein the catalyst is selected from the groupconsisting of Cu—MgO and Cu—MgO—Cr₂O₃ and is prepared byco-precipitation.
 5. A process as claimed in claim 1 wherein the Cr₂O₃is deposited on CuO—MgO by impregnation.
 6. A process as claimed inclaim 1 wherein the mixture of furfural and cyclohexanol is contactedwith the copper based catalyst in vapor phase resulting in thehydrogenation of furfural by hydrogen released due to thedehydrogenation of cyclohexanol.
 7. A process as claimed in claim 1wherein the contacting is carried out in a quartz fixed bed verticalreactor placed in an electrically heatable cylindrical furnace, withabout 1 g of the catalyst packed at the center of the reactor betweentwo plugs of quartz wool being reduced in 6% H₂ and balance He flow at523 K for 4 h followed by lowering the temperature of the reactor to 473K and replacing the H₂/He by pure N₂ gas, the mixture of furfural andcyclohexanol being continuously pumped at a total liquid flow of 1 ml/hinto the reactor, resulting product stream being separated intocyclohexanone and furfuryl alcohol.
 8. A process as claimed in claim 1wherein the contacting is carried out in the absence of externalhydrogen.
 9. A process as claimed in claim 1 wherein the contacting iscarried out at a temperature of about 473 K.
 10. A process as claimed inclaim 1 wherein the contacting is carried out at atmospheric pressure.